In fermentation processes, micro-organisms can be cultivated for instance on moist solid raw materials, such as straw, soy and grains. Such solid raw material, herein further called the substrate, often contains various bacteria and microorganisms that will compete with the micro-organisms to be cultivated and therefore reduce production efficiency.
Hence, the substrate must be disinfected, before it is inoculated with inoculum, in order to avoid contamination by competitor micro-organisms such as other fungi or bacteria. The disinfection of substrates is usually carried out by heating the substrate. Subsequently, the disinfected substrate is cooled to prevent the inoculum from degrading. Such method is described in U.S. Pat. No. 4,922,650. Herein a method is disclosed for continuous manufacturing a substrate for cultivating mushrooms. The substrate is heated and sterilized using saturated steam. Subsequently, the substrate is cooled and spawned. The cooling is performed by scattering water over the solid sterilized substrate using a sprinkler installation. The scattered water does not immediately reach the core of the substrate, making it difficult to regulate the cooling step. Therefore an extra water jacket is used in combination with the sprinkler installation to either heat or cool the sterilized substrate. The procedure is time and energy consuming. Furthermore an installation needed for such a method is complicated, especially since the sterilized substrate must be kept sterile after sterilization. To avoid infections, costly down time of the installation is necessary. FR 2 731 437 discloses a device wherein an gas-dispersed Basidiomycete substrate is heat-sterilised in a heating unit, cooled by a flow of cold air in a cooling vessel and subsequently mixed with inoculum in a mixing device. The condition of gas-dispersion allows a fast and uniform heat-sterilisation, preventing the formation of formic acid in the substrate, as well as an effective cooling. However, FR 2 731 437 does neither disclose nor suggest expansion of the substrate, nor does the heat-sterilisation of the disclosed substrate inherently produce an expanded product.